Due to the use of the Internet Protocol (IP) in the communication network in recent years, the capacity of the communication network has been becoming large. As a result, transmission of a large-capacity data has been required in a wireless communication system as well. Therefore, a wireless communication system which has an Ethernet (registered trademark, the same applies hereinafter) interface and in which large-volume data is transmitted using a virtual transmission path in which a plurality of wireless lines are virtually consolidated into one is becoming the mainstream. A method to virtually integrate a plurality of wireless lines into a virtual transmission path is Link Aggregation, which is defined in Institute of Electrical and Electronic Engineers (IEEE) 802.3ad.
While the wireless communication system having the Ethernet interface becomes the mainstream, the time-division multiplex interface being the existing interface for Synchronous Digital Hierarchy (SDH)/Synchronous Optical Network (SONET) and the like will not be terminated immediately. Therefore, a wireless communication system that involves both the time-division multiplex interface and the Ethernet interface has appeared.
In the wireless communication system that involves both the time-division multiplex interface and the Ethernet interface, there are four conventional techniques described below for performing switching of the line connection, when a failure occurs in a line performing the Ethernet transmission or in a line performing the time-division multiplex transmission.
First, in a wireless communication system in which the path at the connection position of the network with the Ethernetwork is connected redundantly by the current system and the backup system, a technique to switch the path at the connection position from the current system to the backup system has been known.
Next, a technique targeted at a communication network in which the connection apparatus on the Ethernet side where Link Aggregation is used and the connection apparatus on the SDH/SONET side are connected redundantly has been known. In this technique, in such a communication network, a network apparatus having the interface of the SDH/SONET side is provided between the connection apparatus on the Ethernet side and the connection apparatus on the SDH/SONET side. Then, the network apparatus reports whether a plurality of lines used for Link Aggregation are the operating system or the non-operating system to the communication apparatus on the Ethernet side.
In addition, a technique related to the switching control between a current system interface and a backup system interface having different types of network interface, namely the Ethernet interface and the SDH/SONET interface, has been known. In this technique, by converting Automatic Protection Switch (APS) information for Ethernet and APS for SDH/SONET, the reception main signal is switched between the signal received by the current system interface and the signal received by the backup system interface.
Then, in a network that involves a plurality of types of signals such as Ethernet and SDH/SONET and the like, a technique to provide one backup line including a multi-rate reproduction relay board that is capable of handling the transmission speeds of a plurality of types of signals has been known. In this technique, when a failure occurs in a line in which a certain type of signal is transmitted, the transmission speed of the interface board is set to the transmission speed of the signal type, and switching is performed from the line having the failure to the backup line.
In a wireless communication system in which time-division multiplex transmission is performed, when a failure occurs in the current line, data transmission is performed by switching the line connection from the current line in which the failure has occurred to a wireless line provided as a backup line for the current line. That is, in a wireless communication system in which time-division multiplex transmission is performed, at least one unused backup line is provided in advance for the current line to give aid to the failure in the current line.
However, securing the backup line while maintaining it in the unused condition in preparation for the occurrence of the failure in the current line of time-division multiplex transmission is problematic in terms of the efficient use of the frequency, large-volume data transmission and economic efficiency.
Therefore, in the wireless communication system that involves both the time-division multiplex transmission and the Ethernet transmission, when there is no failure occurring in the current line of the time-division multiplex transmission, the use of the unused backup line as a wireless line that constitute the virtual transmission path of the Ethernet transmission may be considered.
As described above, in the Ethernet transmission, to transmit large-volume data, a virtual transmission path in which a plurality of virtual lines are virtually consolidated into one is used. A method to virtually consolidate a plurality of wireless lines into a virtual transmission path is Link Aggregation.
The operation of Link Aggregation includes a degenerate operation and an expansion operation. The degenerate operation of Link Aggregation is an operation to stop the assignment of the frame to a line in which a failure has occurred and to change the frame distribution rule to assign the frame to other lines in which no failure has occurred when a failure occurs in a line constituting the virtual transmission path, for example. In addition, the expansion operation of Link Aggregation is an operation to change the frame distribution rule so that, when a line in which a failure has occurred recovers for example, the frame is assigned the respective lines constituting the virtual transmission path including the recovered line.
In addition, in the Ethernet transmission, to realize the transmission of large-volume data, it is desirable to use Adaptive Coding and Modulation (ACM).
Adaptive Coding and Modulation is a method to make the coding method and the modulation method of the wireless communication system dynamically variable according to the condition of the transmission path.
For example, when the condition of the transmission path deteriorates due to rain and the like, change is performed to 64-Quadrature Amplitude Modulation which is a lower-order modulation than 256-Quadrature Amplitude Modulation (QAM). Accordingly, the transmission of data for which no delay is allowed, such as audio data and video data for example, may be guaranteed.
Meanwhile, when the condition of the transmission path is good, change is performed to 256-Quadrature Amplitude Modulation (QAM) which is a higher-order modulation than Quadrature Amplitude Modulation or Quadrature Phase Shift Keying (4PSK). This makes it possible to increase the number of modulation bits per symbol, and to realize the transmission of large-volume data.
When the modulation methods of the respective wireless lines constituting the virtual transmission path in the Ethernet transmission are different, it is possible to perform assignment control of the traffic volume of the respective wireless lines according to the modulation methods of the respective wireless lines. Therefore, in the Ethernet transmission, to realize the transmission of large-volume data, it is desirable to combine and use Link Aggregation and Adaptive Coding and Modulation.
In the Ethernet transmission using Link Aggregation and Adaptive Coding and Modulation as described above, the transmission capacity of the virtual transmission path in which a plurality of wireless lines are virtually bundled into one wireless line is determined by the number of wireless lines and the modulation method. For example, when the carrier path condition of the wireless lines constituting the transmission path deteriorates or when a device failure and the like of the wireless lines occurs, there is a need to downgrade the modulation method to a lower order, or to reduce the number of wireless lines, and as a result, the throughput decreases.
Therefore, when the backup line of the time-division multiplex transmission is unused, the use of the unused backup line as a line constituting the virtual transmission path in the Ethernet transmission, to increase the number of wireless lines constituting the virtual transmission path may be considered. When it is possible to increase the number of lines of the wireless lines constituting the virtual transmission path, the transmission capacity of the virtual transmission path may be increased, and the decrease in the throughput as described above may be prevented.
However, in the time-division multiplex transmission, it is desirable to perform the transmission with a stable line quality by fixing the modulation method.
As described above, for the wireless line used as both a wireless line constituting the virtual transmission path of the Ethernet transmission and a backup line of the time-division multiplex transmission, when it is used for the Ethernet transmission, realization of data forwarding in a larger capacity using Link Aggregation and Adaptive Coding and Modulation is required. Meanwhile, when it is used for the time-division multiplex transmission, stabilization of the line quality of the wireless line is required.
While the Ethernet transmission in which Link Aggregation and Adaptive Coding and Modulation are used is described above as an example, a similar problem occurs regarding data transmission using a virtual transmission path in which a plurality of wireless lines, modulation methods of which are variable, are virtually consolidated into one line.